"Socialism is about beauty," writes Barbara Castle. Against the discord of the 1984-85 miners' strike, writer Lee Hall conceived the ugly-duckling story of Billy Elliot, the miner's son who discovers ballet and, thereby, finds self-expression and beauty. In Billy Elliot the hit film (2000), directed by Stephen Daldry, you can see Billy, very affectingly, discovering self-expression; but ballet as beauty did not quite emerge. In Billy Elliot the Musical, again scripted by Hall and directed by Daldry, it does.

At one point, amid a chaotic ballet class, Billy (beautifully played on press night by 12-year-old Liam Mower) unwinds from a clumsy multiple pirouette into a sustained attitude derrière effacé- the most marvellous single moment in a new musical for decades. The image, childish but statuesque, says so much: beauty; ballet; the ability of the human to be become the ideal: a multi-dimensionality that is theatrically more real even than the strike, and strangely more serious.

Elton John's music is too often formulaic but about half of this show achieves dramatic poetry of a kind rare in any kind of theatre. It continually transcends realism. A ballet class proceeds amid the battlefield between ranked miners and policemen. Billy, banned from dancing by his father, dances out his frustration against policemen lined up behind their shields.

This socialist musical becomes a lyrical celebration of self-expression set against, and deriving from, multiple expressions of grief: grief for Billy's dead mother, and for the strike's failure. I can't help wanting more, because, in the finest passages, Hall and Daldry have shown that Billy (and socialism) might achieve not only self-expression but beauty too. In this context, self-expression looks like second best.

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